/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.runtime.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * An {@link Iterator} that contains only a single element. The element can be reset such that the iterator can be used
 * multiple times. Initially, the iterator is empty until an element is set via {@link #set(Object)}.
 * 
 * @param <E> The generic type of the iterator.
 */
public final class SingleElementIterator<E> implements Iterator<E>, Iterable<E> {
		
		private E current;
		private boolean available = false;
		
		/**
		 * Resets the element. After this call, the iterator has one element available, which is the given element.
		 * 
		 * @param current The element to make available to the iterator.
		 */
		public void set(E current) {
			this.current = current;
			this.available = true;
		}

		@Override
		public boolean hasNext() {
			return available;
		}

		@Override
		public E next() {
			if (available) {
				available = false;
				return current;
			} else {
				throw new NoSuchElementException();
			}
		}

		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}

		@Override
		public Iterator<E> iterator() {
			return this;
		}
	}
